With the large number of novel proteins being derived from genomics, proteomics, and traditional biochemical approaches there is a tremendous need to develop more efficient methods for the discovery and optimization of small molecule ligands to help determine the biological function of these proteins. Not surprisingly, many of these new targets come from protein families that have received considerable attention ((a) Dolle, R. E., Molecular Diversity, 3, 199 (1998); (b) Dolle et al., J. Comb. Chem., 1, 235 (1999); (c) Dolle, R. E., J. Comb. Chem., 2, 383 (2000) and references therein) in the past such as GPCRs, proteases, and kinases. This presents the combinatorial chemists with the opportunity to take scaffolds developed against a particular protein family member and develop generalized synthetic schemes that allow other family members to be selectively targeted.
A survey of the literature (McMahon et al., Current Opinion in Drug Discovery & Development, 1, 131 (1998); Adams et al., Current Opinion in Drug Discovery & Development, 2, 96 (1999); Garcia-Echeverria et al., Med. Res. Rev, 20, 28 (2000) and references therein) reveals that the vast majority of kinase inhibitor scaffolds consist of planar heteroaryls that present both key hydrogen bond donating/accepting functionality and proper hydrophobicity (FIG. 1).
The purine ring is a prime example of one of these planar heteroaryls. Guanosine and adenosine, two of the most common purines, serve as key recognition and anchoring elements in a variety of cofactors and signaling molecules (e.g., ATP, GTP, cAMP, cGMP, adoMet, adenosine and NADH). Correspondingly, an enormous number of proteins have evolved to recognize the purine motif including reductases, polymerases, G-proteins, methyltransferases, and protein kinases. Despite the abundance of protein kinases (Venter, J. C. et al., Science, 291, 1304 (2001)) (estimated to be encoded by 2 to 5% of the eukaryotic genome) and the high degree of conservation of active site residues, ATP-binding site directed inhibitors have been designed that are highly specific. For example, ST1571 (Druker et al., Nat. Med., 2, 561 (1996); Zimmermann et al., Bioorg. Med. Chem. Lett., 7, 187 (1997); Schindler et al., Science, 289, 1938 (2000)) has been developed as a potent and selective Ab1 kinase inhibitor, and is in use for the treatment of chronic myelogenous leukemia (CML). Screens of purine libraries (Gray et al., Science, 281, 533 (1998) and references therein; Rosania et al., Proc. Natl. Acad. Sci. USA, 96, 4797 (1999); Chang et al., Chemistry and Biology, 6, 361 (1999)) have resulted in the identification of diverse purines that inhibit mitosis, alter cellular morphology, and induce apoptosis. By constructing new purine derivatives, we hope to develop inhibitors of different ATP-dependent proteins, which will be useful for elucidating function and potentially provide starting points for the development of new therapeutics.
Previous syntheses of purine libraries have relied on nucleophilic-aromatic substitution and alkylation chemistry to derivatize the 2-, 6- and 9-positions of the purine ring. One of the primary limitations of this chemistry is the inability to access a large number of pharmacologically relevant derivatives bearing aryl, anilino or phenolic substituents. In addition, the sluggish aromatic substitution of 2-fluoro or 2-chloro substituted purine compounds precludes the introduction of sterically hindered amines or anilines (Chang et al., Chemistry and Biology, 6, 361 (1999)).
Recently, there have been significant advances in methodology for performing palladium-catalyzed C—C, C—N and C—O bond formation reactions with a wide variety of substrates. For example, new phosphine ligands (Wolfe et al., J. Am. Chem. Soc., 121, 9550 (1999); Stürmer, R., Angew. Chem. Int. Ed., 38, 3307 (1999) and references therein; Wolfe et al., J. Org. Chem., 65, 1158 (2000)) have allowed palladium mediated functionalization of inexpensive chloroarenes with boronic acids and amines at room temperature. 1,3-Dimesityl-imidazolin-2-ylidene and its saturated analog, originally developed by Grubbs as carbene ligands for ruthenium-based olefin metathesis catalysts (Scholl et al., Tetrahedron Lett., 40, 2247 (1999); Scholl et al., Org. Lett., 1, 953 12 (1999)), have also been found to be highly effective ligands.
In view of the above, a method using transition metal-catalyzed coupling reaction for the preparation of substituted purines, as well as other planar heteroaryls, would provide access to a greater diversity of substituted planar heteroaryls. Application of this method for the preparation of libraries of planar heteroaryls, which is based on a combinatorial scaffold approach, would represent a significant advance in the art. Surprisingly, the present invention provides such a method and compounds produced by the method.